Methods and systems for complete coverage of a surface by an autonomous robot

ABSTRACT

A robot configured to navigate a surface, the robot comprising a movement mechanism; a logical map representing data about the surface and associating locations with one or more properties observed during navigation; an initialization module configured to establish an initial pose comprising an initial location and an initial orientation; a region covering module configured to cause the robot to move so as to cover a region; an edge-following module configured to cause the robot to follow unfollowed edges; a control module configured to invoke region covering on a first region defined at least in part based at least part of the initial pose, to invoke region covering on least one additional region, to invoke edge-following, and to invoke region covering cause the mapping module to mark followed edges as followed, and cause a third region covering on regions discovered during edge-following.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit under 35 U.S.C. §119(e) of U.S.Provisional Application No. 61/280,678, filed Nov. 6, 2009, the entiretyof which is hereby incorporated by reference.

BACKGROUND

1. Field of Endeavor

What is disclosed herein relates to navigating in an unknownenvironment.

2. Description of the Related Art

It is often necessary or useful to navigate in an unknown environment orsurface so that all or substantially all of that unknown surface istraversed (covered) by a mobile device (e.g., when painting orcleaning). Certain systems and methods for establishing coverage pathsover a surface in an unknown environment are known. However, suchsystems often behave in ways that appear random to users (which may, forexample, make users doubt the efficacy of the cleaning performed by themobile device), often fail to cover readily accessible portions of thesurface promptly or efficiently, and often fail to cover accessibleportions of the surface that are proximate to a first location on thatsurface before attempting to cover more remote portions. Someconventional systems also, fail to thoroughly cover perimeters of thesurface (including the perimeters of obstacles which are internal orpartially internal to the surface).

SUMMARY

Certain embodiments discussed in this application may be used inconjunction with systems and methods disclosed in U.S. Pat. No.7,720,554, filed on Mar. 25, 2005 as U.S. Patent Application2005/0213082, the content of which is hereby incorporated herein in itsentirety by reference. Also, certain embodiments discussed in thisapplication may be used in conjunction with systems and methodsdisclosed in U.S. patent application Ser. No. 12/429,963, filed on Apr.24, 2009, the content of which is hereby incorporated herein in itsentirety by reference.

Disclosed is a mobile device configured to navigate a surface, themobile device comprising a movement mechanism configured to move themobile device from a first pose comprising a first location and a firstorientation to a second pose comprising a second location and a secondorientation; a mapping module configured to update a map representingdata about the surface, the map associating locations with one or moreproperties, the properties comprising properties sufficient to indicate“unexplored”, “traversed”, “edge”, and/or “occupied”; an initializationmodule configured to establish an initial pose comprising an initiallocation and an initial orientation; a first region-covering moduleconfigured to cause the movement mechanism to move the mobile device soas to cover a first region defined at least in part based on at leastone component of the initial pose and further configured to cause themapping module to update the map; a second region-covering moduleconfigured to cause the movement mechanism to move the mobile device soas to cover respective of at least one additional regions and to causethe mapping module to update the map, wherein the first region and theat least one additional regions are non-overlapping; and anedge-following module configured to identify one or more unfollowededges, cause the movement mechanism to move the mobile device so as tofollow respective unfollowed edges, cause the mapping module to markfollowed edges as followed, and cause a third region-covering module tocause the movement mechanism to move the mobile device so as to coverone or more edge-discovered regions if such regions are discovered.

Also disclosed is a method for navigating a surface with a mobiledevice, the method comprising: defining a reference frame using acomputing device, based on at least a component of a first pose of amobile device on a surface having one or more borders and containing oneor more obstacles, the first pose comprising a first position and afirst orientation; exploring, by the mobile device, a first region ofthe surface, the first region determined based at least in part on acomponent of the first pose; exploring, by the mobile device, at leastone first additional region of the surface after exploring the firstregion; maintaining a map of information about the surface in computerreadable memory, wherein at least a portion of the information isobtained by exploring the first region and the additional region;perimeter-following one or more unfollowed perimeter portions whenanalysis of the map indicates one or more unfollowed perimeter portionsexists; and exploring unexplored second additional surface regionsdiscovered while perimeter-following.

Perimeter-following comprises: navigating the mobile device to a firstposition on a first perimeter portion that is unfollowed; following thefirst perimeter portion, relying at least in part on one or more sensorsto determine how to follow the first perimeter portion; updating the mapto indicate that the followed first perimeter portion is followed; andupdating the map with additional information about one or more locationstraversed while following the first perimeter portion. Exploring aregion comprises: navigating the mobile device in the region; updatingthe map to indicate one or more discovered perimeters, perimeterscomprising surface borders and obstacle boundaries, when such areidentified; and updating the map to indicate that traversed portions ofthe surface have been explored.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosed aspects will hereinafter be described in conjunction withthe appended drawings, which are provided to illustrate and not to limitthe disclosed aspects. Like designations denote like elements.

FIG. 1 is a flow chart illustrating an example of a process oneembodiment may use to navigate an unknown area such as a surface.

FIG. 2 is a flow chart illustrating an example of a process anembodiment may use to cover a region, such as when performing theprocess illustrated in FIG. 1.

FIG. 3 is a flow chart illustrating an example of a process anembodiment may use to follow a perimeter, such as when performing theprocess illustrated, in FIG. 1

FIG. 4 illustrates some of the components that may compose an embodimentof a mobile device.

FIGS. 5A-5C is a flow chart illustrating an example of a process anembodiment may use to navigate in a region or a along a portion of aperimeter, such as when performing the processes illustrated in FIG. 2.

FIG. 6 illustrates some of the terminology used herein with an exampleof a “snake” along “ranks” in a “region”.

FIGS. 7-14 illustrate an example application of processes such as thoseillustrated in FIGS. 1-3 and 5 to an example environment.

FIGS. 15A-15B illustrates an example of dynamic resizing of a region.

FIG. 16 illustrates an example of deferred navigation.

FIG. 17 illustrates an example of restricted coverage.

FIGS. 18A-18D illustrates an example of overlapping coverage.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Described herein are methods and systems for navigating an object, suchas a mobile device (e.g., a robotic floor cleaner) in an environment,such as an unknown environment. Certain embodiments may use suchnavigation to completely cover or substantially cover an exposedenvironment or a portion of an environment (e.g., a carpeted oruncarpeted floor).

Certain methods and systems disclosed herein advance the state of theart in how a mobile device with access to information about its relativelocation and orientation (pose) in an environment is able to navigate inthat environment, optionally without a priori knowledge of the layout ofthat environment. A mobile device configured in accordance with certainmethods and systems disclosed herein navigates so as to cover orsubstantially cover an environment (e.g., traverse all or nearly alltraversable locations in the environment, such as a floor, excludingportions that are not traversable because of an obstacle, such as anitem of furniture, a pet, a person, a stair, etc.).

Another example mobile device configured in accordance with methods andsystems disclosed herein achieves such coverage of an environmentpredictably (e.g., it tends to follow a similar or substantially similarroute in the environment on separate coverage efforts, or tend tocomplete coverage or substantial coverage of the environment in the sameor substantially the same amount of time on separate coverage efforts,in an organized fashion). This has the added optional benefit of lettingusers watching the operation of the mobile device be confident that themobile device is thoroughly performing its task in an organized fashion.Further, because certain embodiments operate in a predicable fashion, ifa user needs to walk across the surface being operated on by the mobiledevice, the user can predict what area the mobile device will not betraversing in the immediate future (e.g., in the next minute), andselect that area to walk across.

Yet another example embodiment of a mobile device configured inaccordance with methods and systems disclosed herein achieves completecoverage or substantially complete coverage of a surface or otherenvironment in a reduced amount of time as compared to conventionaldevices (assuming the conventional devices can move at the same speed asthe yet another embodiment).

Some disclosed embodiments can optionally achieve these results whileusing relatively inexpensive amounts of computational resources such asprocessing power, storage, and time, such that the functionalitydisclosed herein can be made available in a relatively compact mobiledevice and/or it can be distributed in affordable mass market consumergoods, including products which perform additional functionality beyondnavigating.

DEFINITIONS

Through the description herein, “localization” may include determiningboth the location of an object in an environment and the orientation ofthat object. A combination of location and orientation is referred to asa “pose”.

“Navigate” is a broad term and is to be given its ordinary and customarymeaning to a person of ordinary skill in the art (i.e., it is not to belimited to a special or customized meaning) and includes, withoutlimitation, determining a route, such as a route from a source locationto a destination location, and moving in an environment (“traversing”)in accordance with that route. Traversing may be performed, withoutlimitation, by moving on wheels or tracks or the like, by flying orgliding, by swimming or floating, by moving logically through a virtualspace, by burrowing through material, and the like. Locations in anenvironment or portions of an environment may be “covered” or“traversed” or “explored” or “navigated” when a mobile devices moves inthem.

“Cover” is a broad term and is to be given its ordinary and customarymeaning to a person of ordinary skill in the art (i.e., it is not to belimited to a special or customized meaning) and includes, withoutlimitation, traversing all or substantially all locations of anenvironment that are traversable and accessible from a startinglocation; traversing sufficient such locations such that all orsubstantially all such locations can be operated upon by a mobile deviceconfigured to perform an operation; and the like. The term “cover” mayalso be applied to a portion of an environment. Illustrative examples ofwhen an environment or portion thereof may be considered “covered”include if at least 100%, 95%, 90%, 85%, or some other thresholdpercentage or proportion of the traversable locations are processed(e.g., traversed or operated upon), or if a threshold amount is coveredor not covered. For example, a vacuum cleaner may be considered to havecovered a room with 100 square feet of accessible surface (e.g., surfacethat is not inaccessible because of an obstacle, such as an item offurniture, a pet, a person, a stair, etc.) if it has traversed at leasta threshold of those square feet, such as 80, 85, 90, 95, or 99. Or, anexample sweeper may be considered to have covered a floor if less than athreshold number of square feet of accessible floor were not swept (suchas 1, 5, 10, or 100), regardless of the total amount of accessiblefloor. In some applications, such as sweeping or vacuuming, it may beparticularly important that a mobile device make explicit coverage of aportion of the environment comprising its “perimeter”. For example,sweeping and vacuuming often cause debris to gather near walls,furniture, or other obstacles. For other applications, for exampledispersing seed or detergent, it may not be necessary to explicitlycover an environment's perimeter so long as the environment is generallycovered.

For convenience, much of this disclosure is expressed in terms of a“mobile device” or a “mobile object”. However, the disclosed aspects maygenerally be used to navigate any type of objects, and one of skill inthe art will understand how the disclosure can be applied to otherobjects, including those that are not independently mobile (such asthose that are transported or carried by something else). By way ofillustration and not limitation, a mobile device may be an autonomous,semiautonomous, or remotely directed floor cleaner (e.g., a sweeper, avacuum, a lawn mower, and/or a mopper), delivery vehicle (e.g., thatdelivers mail in a building, food in a hospital or dormitory, etc.), ormonitoring vehicle (e.g., pollution or contaminant detector, securitymonitor). A mobile device may be equipped with one or more drive motorswhich drive one or more wheels, tracks, or other such devices, where thedrive motors may be under control of a computing device executing aprogram stored in non-transitory memory (e.g., it persists when theobject is powered down or when some other data is overwritten orerased). A mobile device may be configured to navigate for the sake ofnavigation, or it may be configured to perform additional tasks,including without limitation those referenced above, as well as recoding(video, audio, and or other data), mopping, trimming, cutting, anddispensing (e.g., paint, sealant, seeds, fertilizer, or pool cleaner). Amobile device may be a robot configured to perform any of thesefunctions and/or other functions. In sum, “mobile object” and “mobiledevice” are broad terms and are to be given their ordinary and customarymeaning to a person of ordinary skill in the art (i.e., they are not tobe limited to a special or customized meaning) and include, withoutlimitation, the examples mentioned above.

“Environment” is a broad term and is to be given its ordinary andcustomary meaning to a person of ordinary skill in the art (i.e., it isnot to be limited to a special or customized meaning) and includes,without limitation, individual rooms, multiple rooms, corridors, vehicleinteriors, lawns, fields, patios, roofs, sidewalks, roads, bodies ofwater or fluid, swimming pools, floors, ceilings, walls, unenclosed andpartially enclosed outdoor spaces, portions of the preceding, and thelike.

“Surface” is a broad term and is to be given its ordinary and customarymeaning to a person of ordinary skill in the art (i.e., it is not to belimited to a special or customized meaning) and includes, withoutlimitation, that part of an environment which a mobile device navigatesor attempts to navigate, such as a floor, wall, ceiling, ground, fence,interior, top, bottom, side, exterior, and the like. A surface need notbe planar or substantially planar but may include, for example, theinterior volume of an environment (such that navigating such a surfaceinvolves moving in that surface in three dimensions).

Typically, a surface has one or more borders. “Border” is a broad termand is to be given its ordinary and customary meaning to a person ofordinary skill in the art (i.e., it is not to be limited to a special orcustomized meaning) and includes, without limitation, the definingboundaries of a floor such as are established by walls or molding, thedefining boundaries of a surface as set by predetermined dimensions(e.g., a surface may be defined as being 5 meters by 6 meters by 4meters, or being circular with center at a particular location and adefined radius), the defining boundaries of a surface as establishedbased on properties of a mobile device (e.g., because its power orlocalization signals degrade below a threshold when it navigates beyondcertain locations), and the like. It should be understood, unless thecontext indicates otherwise, that a border may be a “virtual” border(e.g., defined by the mobile device), rather than a physical barrier.

“Occupancy map” or “map” is a logical structure associating a locationin an environment or a surface with information and attributes aboutthat location. “Occupancy map” is a broad term and is to be given itsordinary and customary meaning to a person of ordinary skill in the art(i.e., it is not to be limited to a special or customized meaning) andmay be implemented in a wide range of fashions, including withoutlimitation, as a map of locations to properties; as a map of propertiesto locations; using database techniques, using a variety of associativedata structures, or any other embodiment that one of skill in the artmay chose as appropriate for the circumstances and requirements. Thus,it is understood that a map need not be a visible map, but may bedefined via data stored in computer readable memory. As is elaboratedon, a map may correspond to an actual surface with different degrees ofprecisions and/or accuracy. Precision may be affected, for example, bythe use of discrete map cells that correspond to a portion of thesurface. The size of those cells, which may each correspond to a 10cm×10 cm portion of the surface, or a 1 m×1 m portion of the surface(for example—they need not be square or even all of the same size) mayaffect precision by imposing limitations on the granularity of observedproperties. Accuracy may be affected by sensor quality and the like,including various other factors mentions herein. Embodiments may performsome or all analyses discussed herein based on information in a map.

“Explored” locations are those locations or portion of a surface that amobile device was able to traverse. It may exclude, for example,portions of a floor under furniture that a mobile device is unable toslip under or portions of a lawn that a mobile device is unable to reachbecause it is unable to travel through mud or water. In othercircumstances, (e.g., if the mobile device is suitably small, configuredfor ‘off-roading’, or able to navigate water), then these areas maypotentially become explored areas. Explored area may also excludeportions of the surface that the mobile device has not yet traversed butwhich are traversable.

“Occupied” locations may include those portions of a surface that amobile device is unable to traverse. Portions may be occupied if thereare physical obstacles that prevent the mobile device from traversingthat portion, if a property of the surface renders a portion of itinaccessible, if a power supply or control signal or other necessaryelement of the mobile device's operation does not function adequately inthat portion, and the like.

A “snake” is a type of path or route by which some mobile devices maytraverse a portion of a surface. By way of illustration, and notlimitation, a mobile device may be said to have “taken a snake in aportion of a surface” or it may be said that “a snake is available for amobile device to follow”. A mobile device following such a path is“snaking”. This term is elaborated on more completely below.

“Frontier” refers to a boundary between an explored and unexploredportion of a surface. In some embodiments, a “snake frontier” refers toa frontier selected or eligible for snaking into. In some embodiments, amobile device will navigate into the unexplored side of a frontier bysnaking. In some maps, a frontier may be comprised of traversed orexplored locations which have unexplored locations neighboring them. Inother maps, a frontier may be comprised of unexplored locationsimmediately adjacent to explored or traversed locations.

A “perimeter” of a surface may include borders of the surface as well asthe edges of any obstacles in or partially in the surface. For example,the footprint of a piece of furniture or the outline of a sleeping petmay be part of a perimeter. So too might the three dimensional contoursof a dense rock in an underground environment where the traversablesurface comprises less dense dirt and a mobile device is unable totraverse through the rock.

An “edge” is a boundary between an explored and occupied portion of asurface. For example, an edge might surround the trunk of a tree in alawn-mower embodiment. Some frontier locations may also be edgelocations if an occupied location is considered unexplored or if thoselocations are part of both a boundary with occupied locations andanother boundary with unexplored locations. Embodiments may definefrontiers, edges, and/or perimeters with respect to a map, based atleast in part on at least some of the properties of at least some of thelocations in the map.

Methods and Systems for Navigating For Coverage

Example embodiments will now be described with reference to certainfigures. The following detailed descriptions are generally made withreference to a two-dimensional surface such as a floor or wall. Thisdisclosure can readily be extended by one of skill in the art to applyto movement and surfaces having three dimensions.

Overview of a Coverage Process

FIG. 1 is a flow-chart illustrating an example control process 100 forcovering a surface. The example process includes the following coveringphases: (i) region-based covering; and (ii) perimeter covering orfollowing. Region-based covering is generally directed to coverage ofaccessible portions of a surface, while perimeter covering is generallydirected to coverage of a perimeter of a surface (borders and edges).

As shown in FIG. 1, at state 110 the current pose P of the mobile deviceis obtained, for example using a signal based localization system or adead reckoning system. In the illustrated embodiment, the coverageprocess 100 establishes a starting location and principal axes ofnavigation (coverage direction) defined at least in part by P. In oneembodiment, a user can establish P by placing a mobile device onto asurface. In another embodiment, the mobile device might assume aparticular starting location and/or orientation on its own. Such anembodiment may use, for example, the systems and methods of U.S. Pat.No. 7,720,554 to identify and assume a pose. In yet another embodiment,the mobile device may presume or require that it has been placed in aparticular initial pose, with subsequent processing relying on thatpresumption. In still another embodiment, the mobile device may traveluntil it encounters an obstacle, optionally identify that obstacle as awall or other border, and establish P based on the apparent positionand/or orientation of the obstacle.

In one embodiment of process 100, the starting location is defined,logically, as (0, 0) and the starting orientation is defined, logically,to be π/2 radians (90 degrees). That is, the reference frame orcoordinate system used by the embodiment is relative to the initial poseP. Any other initial location or orientation definition could be used,and the description below would be adjusted accordingly.

In accordance with process 100, a mobile device first performsregion-based coverage to the right of this starting location at state120 by invoking a region based coverage process such as process 200 ofFIG. 2 with a start condition set to “cover to right” in state 115. Oncethe mobile device finishes region covering to the right, it performs asimilar covering action to the left of the initial starting location Pby setting the start parameter to “cover to left” at 125 and invokingprocess 200 at 130.

After covering to both the left and the right, there may still benon-perimeter portions of the surface that the mobile device has notcovered. For example, one or both of the cover-left and cover-rightroutines may directly or indirectly impose a maximum on the distance themobile device can travel or on the amount of surface it may cover. Also,one or both of the routines may be interrupted, such as by the need forthe mobile device to charge or to have consumables replaced, by a userpausing operations, or by an exception such as may be associated withthe mobile device entering an error state including but not limited tolosing traction, being stuck in a recess or on a peak stuck, or becomingwedged. Illustrated process 100 delegates checking for potentialportions of the surface that have yet to be covered to process 200,which it invokes at 140 with the start parameter set to “cover anywhere”at state 135. In other embodiments, this check could be performed byother processes or at other times. For example, it could be a concludingstate of process 200 when it is invoked with “cover to left” or it couldbe performed or invoked by process 100 directly.

An example process illustrating how such portions of the surface may beidentified and covered is discussed below, in the context of FIG. 2. Ifsuch a portion is found, the region-based covering process 200 returnswith a value of “region covered” at 143 and process 200 is again invokedwith start set to “cover anywhere”. If no such portion is found, theprocess 200 returns with a value of “no frontiers” at 141. If thishappens, the mobile device should have substantially covered theidentified accessible or traversable portions of the surface and createda fairly complete map of those portions. Process 100 then continues tostate 150, where it invokes a perimeter covering process 300.

An example of a perimeter covering process 300 is shown in FIG. 3 and isdiscussed in more detail below. At a high level, such a process 300analyses the map or otherwise selects an un-followed edge or border(perimeter) to cover or navigate along, navigates along that perimeter,updates the map as it does so, and determines if continued perimetercovering is necessary.

Process 100, as illustrated, handles at least three return values orstates of process 300. If process 300 terminates with status “snakecreated” as at 155, then a new unexplored portion of the surface wasdiscovered and a snake into that portion was identified. In that case,process 200 is invoked at state 140 after the start parameter is set to“cover created snake” at state 143. If process 300 terminates withcondition “perimeter covered” then process 100 may cease. Alternatively(and as illustrated), in response to “perimeter covered” process 100 mayloop back to invoke region-based covering process 200 with “coveranywhere” via states 135 and 140. This is an extra precaution in someembodiments to account for situations where noise in the map (such asfrom sensor inaccuracies or anomalies, defects or deviations in a mobiledevice's mechanical aspects, or other errors in localization) causes themobile device to fail to correctly map or correctly characterizelocations and thus fail to identify and explore one or more frontiers.If this precautionary run of process 200 identifies no frontiers,process 100 again invokes perimeter covering process 300, which maycause the mobile device to follow another perimeter that has not beenperimeter-covered. Yet another alternative is for process 100 to loopback directly into perimeter covering process 300 for an additional passwhen a first invocation of that process concludes with condition“perimeter covered”, without an intervening invocation of region-basedcovering process 200.

If process 300 concludes that there are no perimeter frontiers in themap, it may return with condition “no perimeter frontiers”, as at 157.The mobile device may then cease its coverage control routine, as at160.

At this point 160, a mobile device may signal (e.g., through an audible,visual, tactile, or electronic communication to a user, through a wiredor wireless signal or other interface to an invoking device, and/or to amonitoring application) that it has completed covering and/or an action,such as cleaning, associated with covering. Some mobile device maynavigate to a charging station, storage bin, their initial location orpose, or a predefined next location or pose. Some such embodiments maychoose one or more behaviors to take upon conclusion based on one ormore conditions. For example, an embodiment may return to a start poseor location unless a next location or pose has been set. Anotherembodiment may send an email indicating that coverage is complete,return to a charging station if it is in need of charging, and otherwiseproceed to cover the surface again (e.g., return to state 110, perhapswith a different starting pose than the previous time it performed state110).

To provide predictable and consistent behavior across different runs, amobile device optionally advantageously invokes region-based coveringprocess 200 at states 120 and 130 with the same parameters in the sameorder each time (although in other embodiments, different parametersand/or orders may be used from iteration to iteration, as discussedbelow). Thus, when such a process 100 is run, the initial behavior ofthe mobile device will be consistent such that if it is placed in (orassumes) the same initial pose (or perhaps one a few inches orcentimeters away, but with a very similar orientation) then it will atleast begin to cover the surface in the same or substantially the samemanner each time (although noise and other factors discussed above, aswell as changes in the position of obstacles, may affect the routeultimately taken and the manner in which the surface is covered). Otherembodiments may randomly or pseudo-randomly invoke process 200 witheither “cover to left” or “cover to right” first. Yet other embodimentsmay be configured with sensors that determine if an obstacle isproximate in the left or right direction and first cover in thatdirection or the other direction.

In cases where perimeter covering is not required to successfullycomplete a mobile device's non-navigational function (such as perhapsthe dispensing of a detergent) process 100 may conclude after theregion-based covering phases are completed and before invocation ofperimeter covering at 150. This may result in less than completecoverage of the surface because some regions (e.g., those whose presencemay be indicated by perimeter covering process 300 returning with aresult of “snake created”) may remain undiscovered and thus untraversed.

Region-Based Coverage

FIG. 2 illustrates an example implementation of an example region-basedcoverage routine or process 200. As implied by the discussion above,process 200 may have several possible starting points (e.g., at leastfour possible starting points (states 205, 215, 225, and 250)), whichare selected based at least in part on the value of a start condition.An alternative, not illustrated, is for a process such as process 200 tohave a single entry point, to evaluate a start condition, and to proceedaccordingly. The illustrated embodiment of the region-based coveringroutine 200 has two exit conditions, set at states 295 and 245

As mentioned above, a controlling process, such as process 100, mightfirst invoke process 200 with start parameter “cover to right”, theninvoke it with “cover to left”, then invoke it with “cover anywhere”,and then invoke it with “cover created snake”. In other circumstances orembodiments the process 200 may be invoked with similar parameters butin a different order, for example as mentioned above. Also, aselaborated on below, additional or alternative parameters are used bysome embodiments. For example, “cover bottom” and “cover top”, “coverleft at 45 degree angle”, “cover first 30 degrees”, etc. In general, thedescribed left/right cleaning can be generalized with sectors spanning adefined angle. As described, the angle is 180 degrees, but sectorsspanning other angles, including but not limited to 120, 90, and 60could be supported in this fashion. Process 200 also makes use of avariety of other parameters. One of ordinary skill in the art willunderstand that a wide variety of factoring and parameter passingstrategies can be used.

When invoked with “cover to right” at 205, covering parameters are setat 210 so that the starting location is the initial location of themobile device (the location component of P) and the coverage or coveringdirection is set to the initial orientation of the mobile device (theorientation component of P) rotated by negative π/2 radians (90 degreesclockwise). When the start condition is set to “cover to left”, process200 is entered from starting point 215, and at state 220 the coveringparameters are set as the mobile devices initial location (again) andthe mobile devices initial orientation rotated by positive π/2 radians(90 degrees counter-clockwise).

A consequence of these settings is that some processes, such as thoseillustrated, cause the mobile device to first move in the direction inwhich it was placed on the surface, proceed to cover a portion of thesurface on one side of the line in which it first moved, return to thatinitial location, and proceed to cover a portion of the surface on theother side of the line along which it first moved. Some such embodimentsmay be advantageously predictable, have esthetically pleasing navigationroutes, and perform ancillary tasks (such as cleaning) in accordancewith a user's expectation because they initially and repeatedly operatearound the initial location (which may be a location of particularimportance or relevance to a user).

A subset 212 of process 200 uses a starting pose SP and a coveringdirection D, which are established at 255. Direction D determines theorientation of the covering actions (e.g., navigating or snaking) thatcan be selected within the region, which in turn determines thedirection in which the mobile device covers or navigates. For example,although the mobile device may move in a variety of directions, it maygenerally cover surface in the direction D. The starting pose SPdetermines the position the mobile device starts covering from.Optionally, the covering direction D and the starting pose heading(orientation) are orthogonal to each other. Another parameter that maybe set at state 255 is MAX, the maximum number of regions that themobile device should try to cover while proceeding in direction D. Afterinitialization, at state 260 the current region is set to be Region 1.

At state 265, a covering region (initially, region 1) is created. Aregion is a logical structure comprising a virtual bounding box. It maybe defined based on the direction D and the starting pose SP. In oneembodiment, a region is created as part of the map, which storesdefining parameters of the region (including, e.g., its region number,D, and SP). Regions may be static or dynamic. Some mobile devices mayuse both static and dynamic regions during the same covering processwhile other embodiments may use only one or the other during a givencovering process. Still others may only ever use one or the other.

With a static region, the location and dimensions of the region withrespect to SP and D may be established before the mobile device beginscovering the region. For example, a static region may be defined to havea pre-defined size (such as 5 feet by 5 feet) and location relative toSP (e.g., edge-centered around SP or to have a vertex on SP). In oneembodiment for mobile devices that clean floors in American homes, thestatic region size is preset to be about 7 m long (along the “ranks”direction, discussed in more detail below), 1.5 m wide, andedge-centered around SP (although the static region may have smaller orlarger dimensions).

A dynamic region is initialized with dimensions, preferably dimensionsthat are expected to be relatively small compared to the dimensions ofthe surface (e.g., 0.5 meters by 0.5 meters for a mobile device intendedto operate on the floors of American homes) and allowed to expand,perhaps to a predefined maximum size/dimension(s), so as to adapt theregion according to the environment. A dynamic region may, like a staticregion, have a predefined location relative to SP.

Static and dynamic regions are illustrated in FIG. 15A and FIG. 15B. InFIG. 15A, a mobile device starting at pose 1530 snakes within room 1510and is confined to static region 1510. The snake 1540 it follows showsthat when it detected that it was leaving the region 1520 it moved on tothe next rank of its snake, even though it was still in room 1510. Incontrast, FIG. 15B shows that a mobile device following a similar path1560 in a dynamic region 1550 will reach the south wall of room 1510because the region 1550 expands when the mobile device reaches itssouthern edge but is still able to proceed into unexplored andunoccupied areas.

Map analysis related to snake frontier enumeration, selection, and/oridentification may be restricted to the current region. Some embodimentsmay be configured so that at times they conduct a global frontierenumeration or otherwise enumerate frontiers in previously coveredregions as well as or in addition to the current region. Also optionallyrestricted to the current region in some embodiments is the movement ofthe mobile device itself. Other embodiments are not so restricted, butthe restriction has an advantageous result of causing a mobile device totry to cover the current region before moving elsewhere. For example, atstate 270, a snake S is sought within the current region.

If a snake S meeting constraint SC1 exists, the mobile device startssnaking at state 275. Other embodiments may implement a covering action(navigation) other than snaking. As the mobile device snakes, the map isupdated to record, for example, locations that have been traversed,where obstacles have been detected, and where borders appear to exist.Snaking is discussed in more detail in the context of FIG. 5, below.

Different conditions can cause the mobile device to quit the snakeaction or other traversing action. For example, the mobile device mayreach the end of the current region (e.g., the next rank for the snakingprocess is outside the region and the region, if dynamic, is unable togrow any further), it may reach a border of the surface, an essentialsignal (such as a power or localization signal) may become weak, aphysical limit (such as the length of a cord) may be reached, or anobstacle may be sufficiently large or suitably arranged so as to blockan entire snake rank and prevent a mobile device's navigationalprocesses from causing the mobile device to navigate around it. When thesnake action is finished, a mobile device determines what action to takenext. The mobile device may do so as at state 280, by analyzing the mapand identifying a suitable frontier, such as the one closest to themobile device. An appropriate frontier preferably satisfies constraintSC2. These constraints may include having a minimum rank length (forexample, one robot diameter or 20 centimeters) and having a dominant(general) direction or orientation of D. Restricting D in this way tendsto result in a mobile device continuing to cover or explore in the samedirection (D) as before. Some embodiments may select a frontier withdominant direction other than D, including directly opposite to D. Someembodiments may do so only if that frontier has a minimum rank lengthlonger than any frontier having a dominant direction of D. An embodimentmay advantageously explore a region with a dominant direction other thanthe current dominant direction because sometimes the only way to enter aregion is from the a particular initial vector.

If at least one such frontier passes/satisfies constraints SC2, a“valid” snake action exists and it is selected as the candidate S for anext loop to state 270. If no such snake exists, then if the currentregion is not MAX (e.g., if the embodiment's limit for the number ofregions for that invocation of process 200 has not been reached), thecovering region counter is incremented at state 290 and a new regionwith a new bounding box is created at state 265. The new bounding boxand other constraints may limit subsequent map analysis and snake actionas just described.

If the mobile device has already reached the maximum allowed regions MAXat 285, then progressive region covering terminates at 295 with a statusof “region covered”. Some embodiments may have a system level MAX, suchthat the total number of regions created cannot exceed it, while othersmay have a MAX for particular invocations of progressive region-basedcovering, or have none at all. Some embodiments may impose a MAX of onetype or the other for performance reasons, such as to limit the amountof memory consumed or the processing time required. Limits on MAX mayresult in a lower degree of coverage, if other properties (such as thesize of regions) are not adjusted accordingly.

When process 200 is invoked with start parameter set to “cover anywhere”at state 225, the mobile device also analyzes the map to identifysuitable frontiers at state 230. Potential frontiers are evaluatedagainst constraints SC1 at state 235. A frontier is selected (e.g., theclosest to the current location of the mobile device or the one thatwould be least expensive to reach given an expense calculating orapproximating function such as power consumption or time to reach) andcorresponding initial parameters are set (based, for example, on theproperties of snake S, the current pose of the mobile device, and thestatus of the map) at 240. Processing then proceeds per subset 212 atstate 255. Depending on the parameters set at 240, the starting pose SPmay be the current pose of the mobile device at the time, and thedirection D may be set to any value, including for example the previousD, the current orientation of the mobile device, or the dominantdirection of the frontier to be explored.

Constraints SC1 and SC2 may limit the mobile device to ensure goodlocalization or other behavior. For example, appropriate constraints cancontribute to a mobile device cleaning broad open areas of the surfacein proximity to the starting location before exploring areas with morelimited accessibility and/or which are further from the startinglocation. Constraints SC1 and SC2 may include a length restriction, suchthat a snake must have an initial rank length of at least a certainthreshold, such as 20 cm, 1 meter, or other values (or, e.g., a mobiledevice diameter, 1.5 or 2 mobile device diameters, or some othermultiple of a mobile device diameter). Constraints SC1 and SC2 may ormay not include orientation restrictions. While constraint SC1 may ormay not have a minimum length, it advantageously has one that is longerthan that of a length constraint of SC2 if SC2 has a length constraintFor example, if an embodiment has a minimum SC2 length check of 0.5meter then that embodiment may preferably have an SC1 length check of1.5 meters. There need not be a correlation between the two lengthchecks, but in some embodiments the minimum length for SC2 willcorrespond to be approximately the diameter of the mobile device (orapproximately the largest cross section orthogonal to the direction ofmovement) and in some embodiments the minimum length for SC1 will beapproximately three times that measure. In other embodiments this ratiowill be different, and in other embodiments there may be no suchcorrelation.

Having the length requirement for SC1 be larger than that for SC2 helpsaccount for the observed possibility that errors in localization ormapping that have accumulated during subset 212 might result in the mapindicating that small snake frontiers exist even though, in fact, themobile device has already covered those portions of the surface. On theother hand, during subset 212, selecting smaller frontiers has beenobserved to help ensure the mobile device more completely coversaccessible portions of the surface and helps reduce the presence offrontiers in the map that might otherwise be addressed by subsequentprocessing.

Recall from FIG. 1 that states 135 and 140 are repeated in theillustrated embodiment so that process 200 is invoked with startparameter “cover anywhere” until no snake S satisfying SC1 (oroptionally less than a threshold number of snakes satisfying SC1) isfound and process 200 exits with condition “no frontiers”. Thus, themobile device continues to select frontiers from the map while at leastone such frontier exists.

Illustrated process 200 may also be invoked at state 250 with start setto “cover created snake” if a snake is found during perimeter covering.The parameters for covering may be set as they are when a snake S isfound during state 235.

What has been described so far and what is illustrated in other figuresimplies regions of rectangular shape, the present methods and systemsmay be applied to regions of any shape. For example, the surface can bedivided in three or more regions radiating out of the initial mobiledevice location. In such an example, the terminology “cover to left” and“cover to right” would be modified to something such as “cover sectorn”, where “n” identifies a sector. Other parameters, such asorientations, region dimensions, and minimum lengths, may also beadjusted to account for the changes in geometry in these circumstances.

Snaking Action and Navigation

Above, references have been made to snakes, snaking action, andestablishing snake parameters. For example, in state 275 of process 200in FIG. 2. Snaking action may be implemented by a process such asprocess 500 illustrated in FIG. 5.

Generally, snaking action (snaking) may optionally be limited by thecurrent region. Also, as the mobile device traverses the surface, a mapis updated with information including but not limited to some or all ofthe following: location of obstacles, traversed portions of the surface,hazard portions (e.g., changes in surface material, altitude changes,locations of high wind or with a particular chemical presence, or othercharacteristics that may constitute a hazard for a given embodiment),the presence/absence of a localization signal, and/or the like.

The input parameters to the illustrated snaking process 500 may includethe snake origin location and orientation, the direction (heading ororientation) of a desired snaking action, and the initial length andspacing of ranks. In the illustrated embodiment, the snaking directionand snake origin orientation are with respect to a single global map.These parameters, such as may be used in an example embodiment, areillustrated in FIG. 6. A region with boundaries 610 has beenestablished. The origin pose of the snake (i.e., the orientation of themobile device at the beginning of the snake action) is at pose 620,which is set, without loss of generality and to simplify the disclosure,to have a logical north orientation. Other orientations, includingsouth, east, west, and oblique, may also be used. The illustrated ranks630 are orthogonal or substantially orthogonal to the axis of theinitial pose, but other embodiments may have ranks which run oblique oreven parallel to the axis of the initial orientation. In suchcircumstances, certain of the directions and other parameters referencedin FIG. 5 and the associated discussion of that figure would changeaccordingly. The ranks 630 are parallel to each other and, in theillustrated embodiment, evenly spaced with rank spacing 650.

In some embodiments the rank spacing 650 is approximately 0.5 meters. Inother embodiments ranks may have a defined but non-constant spacing.Rank spacing 650 may be related to the dimensions or functionalproperties of the mobile device (e.g., the suction range of a mobiledevice vacuum or the dispersant range of a mobile device seeder) suchthat the portion of the surface affected (traversed or operated upon) bythe mobile device while following one rank overlaps with the portion ofthe surface affects while following the next rank. Overlap may,depending on an embodiment, be greater or lesser and may depend oncontext. For example, if a sparse coverage is desired, such as duringsome types of planting or perhaps when distributing a material that willdisperse into the environment, the rank spacing may be greater, such as1.5 or 2 times (or more) the size of the mobile device or 1 or 2 meters.If repeated treatment of a surface is advantageous or not harmful, suchas when mowing a lawn, for example, then rank spacing may be set to alower level, such as 0.25 meters or less. In some embodiments, such asthose that are illustrated, a smaller rank spacing may result incoverage requiring more time and/or more computational resources. Rankspacing may also be relative to one or more mobile device dimensions,such as 0.25, 0.5, 1.0, 1.25, 1.5, or 2.0 times a dimension.

The length of a rank is measured along the direction 640 orthogonal tothe direction of rank spacing 650. Arrows 660 indicate the directionalong the rank a mobile device will travel when snaking. Thus, themobile device in FIG. 6 may proceed north to Rank 1, turn 90 degreesclockwise, and proceed along Rank 1 until the region boundary 610 isreached. The mobile device may then rotate 90 degrees counterclockwiseand travel until it reaches Rank 2. At that point the mobile device mayrotate 90 degrees counterclockwise and proceed to travel along Rank 2.In this fashion the mobile device “snakes” along the ranks, traversingeach rank in the opposite direction of the way it traversed the previousrank and generally progressing in a northerly covering direction. Thisexample of snaking action, which is but one navigational strategy anembodiment may use to traverse a region, is elaborated upon in thecontext of FIG. 5.

Turning back to FIG. 5, which is decomposed into FIGS. 5A, 5B, and 5C,an example of a snaking action process is outlined. At state 502 theroutine starts. In state 504, the snake parameters are set and thecurrent rank is set to the first rank. In state 506 the mobile devicemoves to the snake origin pose if the mobile device is not alreadythere. In state 508 the mobile device moves along the current rank inthe direction of traversal associated with that rank. As mentionedbelow, in some embodiments the movement of mobile device may not bedirectly along the current rank but may generally follow it while movingabove and/or below the rank. In state 510 the mobile device checks if ithas reached the end of the rank or crossed a boundary of the currentregion. If either condition is true, in state 511 the map is analyzed tosee if the portion of the surface beyond the end of the rank isunexplored.

If the condition is true, and the mobile device has reached the end ofthe rank but not a boundary of the region, the current rank length maybe extended by a predefined increment in state 513 and the routine loopsback to state 508 to continue moving along the, now longer, currentrank. The rank length increment need not be predefined and may, forexample, be based on a previous length increment, the previous length ofthe rank, the distance between the current end of the rank and a borderof the region, or the like. In an embodiment with dynamically sizedregions, the length of the region may be similarly extended at state 513if a region boundary is reached. If a rank can not be extended at state513, then a frontier may be defined. Subsequent analysis of the map,such as in the processes described above or in the perimeter coveringprocess described below, may expose that frontier for snaking, or it maybe explored during the performance of those processes.

If condition 511 is false (because, e.g., the portion of the surfacebeyond the end of the rank was part of a previously explored region oris an identified obstacle), then in state 512 the current rank isincremented by one and the direction of traversal is inverted withrespect to the previous direction. In some embodiments, rather than moveto the next rank, the mobile device may instead skip a rank and move tothe second or even higher rank. In state 514 the mobile device checksfor exit conditions, including having crossed the top (e.g., logicalNorth) region boundary or having lost a localization signal during thecurrent rank traversal. If any (or a specified subset) of suchconditions is true and can not be remedied (e.g., by dynamically growingthe region or by using an alternative signal or means of localization),the routine exits in state 516 and returns, e.g., to the region coveringstate 280 of FIG. 2. In some embodiments, the critical checks of state514 are run on an interrupt basis or on a scheduled basis, as well as orinstead of at a set point in the performance of a process such asprocess 500. If condition 514 is false, the mobile device continuesalong the current rank per state 508.

If condition 510 is false and the mobile device has been moving along arank, then it is possible it has encountered or sensed an obstacle. Thisis checked for at state 518. If condition 518 is false (no obstacle issensed), the mobile device continues moving along the current rank perstate 508. However, if condition 518 is true, then a navigation methodsuch the illustrated snaking handles the detection of an obstacle in oneof three ways, based at least in part on an analysis of the map at state520. The illustrated options are (1) to exit process 500 at state 524,(2) to follow the edge of the sensed obstacle in the logical northdirection at state 522, and (3) to follow the edge of the sensedobstacle in the logical south direction at state 526.

The decision at state 520 can be made using many different criteria. Inone embodiment, one of the three options is selected using predefinedprobabilities so that each is selected approximately ⅓ of the time oranother predefined proportion. In another embodiment, a random orpseudorandom algorithm may determine which option is selected. In yetanother embodiment, the probability of selecting an option changes overtime based, for example, on previous results (e.g., if that option leadsto continued snaking, then the probability of choosing that option inthe future is increased, and if that option leads to exiting the snake,then the probability of choosing that option in the future isdecreased). In another embodiment, the map is analyzed to simulateseveral possible paths or routes, both north and south, that would takethe mobile device from the current location (i.e., the one at the edgeof the obstacle) to navigate around the obstacle to either rejoin thecurrent rank or to traverse to the next (higher) rank (if, e.g., theobstacle extends the remainder of the traversable length of the currentrank). Various criteria, including the geometric length of the path andthe resources consumed during the route (in terms of time, computationalresources, and power, for example), can be used to select a desiredpath, and thus whether to proceed north in state 522 or south in 526.

At state 528 the mobile device checks if, while following the edge ofthe obstacle in the north direction, it has intersected the next rank.If it has, the routine loops back to state 512. In other embodiments themobile device may remember this location on the next rank and continuearound the edge of the obstacle until another indicator is reached, suchas the second rank up, a region boundary, or an indication that theobstacle is extending deeper into the region and the mobile device istherefore moving, for example, east when it was moving west when itoriginally encountered the edge. At each such decision point (or at asubset of decision points), some embodiments may decide to continuetrying to go around the obstacle and some embodiments may return to theremembered location. If the mobile device is able to return to theoriginal rank in such an embodiment, or if, as in state 532 of theillustrated embodiment, the mobile device reaches the current rankbefore reaching the next rank, process 500 resumes at state 508, wherethe mobile device rejoins the current rank and continue moving along it.

If condition 532 is false (implying the mobile device is between thecurrent rank and the next rank), the mobile device checks if, whilefollowing the obstacle's edge in an initial northerly direction, it hastravelled too far north, meaning the travelled distance in the northdirection has surpassed some predefined threshold such as ⅔ of ½ of rankspacing. If condition 536 is true, the routine exits at state 542; iffalse, the mobile device checks for having crossed the region boundariesin state 538. If the mobile device has crossed the region boundaries,then the routine exits at state 542.

In other embodiments, the mobile device might not exit the routine 500if 536 or 538 is true, but may instead navigate back to the location onthe original rank at which it encountered the obstacle, or any othervalid location within the region and not too far north, and return tostate 520, making a decision based on the new information gained andrecorded in the map. In the illustrated embodiment, if the test at 538is false then the mobile device remains where it is and the routineloops to state 520, where the map is analyzed in light of the new mobiledevice pose and new information added to the map during the recentnavigation. In other embodiments, the mobile device may return to any ofthe traversed locations between the current one and that where it firstencountered the edge before resuming the routine at state 520.

Similar and analogous states may be followed if option (3) is chosen atstate 520 and routine 500 causes the mobile device to follow the edgesouth in state 526. In state 530 the mobile device checks if it hasintersected the current rank. If the mobile device has intersected thecurrent rank, the routine loops back to state 508; if it has not, themobile device checks in 534 if it has travelled too far south which maybe defined analogously to too far north (although some embodiments mayuse different definitions for too far north and too far south). Too farsouth may also be defined as having reached the previous rank. If themobile device has moved too far south, the snaking routine 500 exits atstate 542; if it has not, the mobile device performs the previouslydescribed check at 538.

Other strategies may be deployed to navigate within a region so as tocover it. For example, a mobile device may chart a path corresponding toa circle, square, or other geometric shape that spirals outward from anorigin point. Also, for any navigation method with an underlying pathtactic (e.g., ranks or the spirals of a spiral shape, a mobile devicemay follow that path in a variety of fashions. It may, for example,follow the path as discussed above and elaborated on below. A mobiledevice may also deviate off the path in either direction (e.g., “above”or “below”). For example, it may sweep out a sinusoidal pattern centeredor substantially centered on the path, or a vine-like motion describedby alternative back and forth motions, biased in the direction of thepath, such that on average the mobile device moves along the path. Insome embodiments that deploy these navigational strategies, the mobiledevice is generally following the path, while covering parts of thesurface not directly on the path, perhaps for reasons associated withthe functionality of the mobile device (e.g., sweeping or mopping) orfor limitations imposed by the mobile device's locomotive capabilities.Embodiments may implement a number of variations of this basic snakingroutine. In some embodiments that deploy a snaking strategy, instead oflinearly following a rank, a mobile device may follow it on average, buttraverse above or below a rank. These and other motions can be used tocover a region.

Perimeter Following/Covering

FIG. 3 illustrates an example process for an embodiment of a perimeterfollowing routine 300. Some embodiments may invoke routine 300 at leastin part because following the edges of previously discovered obstaclesand/or the surface borders has a functional value. An example is amobile device configured to perform dusting with an electrostatic pad.Performing perimeter dusting towards the end of the dusting (covering)process allows the mobile device to collect any dust or debris that waspushed towards the perimeter during the course of region-based cleaning.Another example of perimeter covering's functional value is that it canhelp appropriately configured devices clean baseboards and the bottomsof furniture.

Some embodiments may invoke routine 300 to help obtain more completecoverage through discovery of previously unexplored portions of thesurface. For example, in cluttered rooms the layout of the accessibleand traversable portions of the floor is such that large traversableportions of the surface are accessible only by small connecting portionsthat are just slightly wider than the width of a mobile device. Duringperimeter covering, portions of a surface, such as some of these smallconnecting portions that may have been missed during the region coveringphases, are identified. If such portions are identified, the mobiledevice may explore them by entering into a new snake covering routine.One way such connecting portions may be missed, for example, is if theyoccur between two ranks at the opposite end of the ranks from the endwhere the mobile device moves from the first rank to the second rank.Perimeter covering is also an opportunity to discover if previouslyidentified obstacles have been moved or removed.

Recall from the discussion of FIG. 1 that perimeter covering may beinvoked by the illustrative covering routine 100 at state 150, afteranalysis of the map indicates that there are no further frontiers toexplore (e.g., region covering process 200 has exited at state 245 withexit condition “no frontiers”). At this point, the mobile device hastypically constructed a map of most of the surface after havingperformed region based covering in it. The mobile device begins theperimeter covering phase 300 by analyzing the map and enumeratingfrontiers satisfying constraint PC1 at state 310. Constraint PC1describe frontiers which are eligible for perimeter covering. Forexample, PC1 might be such that it includes frontiers that are betweenexplored and occupied locations and/or explored and unexplored locations(e.g., locations not traversed during snaking) which have not beenperimeter-covered and which are within the surface.

Constraint analysis is performed against the surface as known by themobile device or other processor. For example, it may be performedagainst or using a map. A map may have mark location on the surface indiscrete cells of some defined size. The size of a cell, which can varyfrom embodiment to embodiment, may range from 0.5 cm or smaller squaresto 0.5 meter or larger squares, depending on the context (including thefunctions of the mobile device, the environment, and the sensors on themobile device, for example). Cells need not be square, or even regular,but may be circles, rectangles, hexagons, or other closed shapes. Insome embodiments, it is these cells that are associated with propertiessuch as occupied, explored, and the like.

Although other embodiments may use other structures for maps, thisnomenclature of cells with properties helps illustrate another possiblelimitation in PC1, which is based on length as determined by cell count.When performing the analysis at state 310 the mobile device may beginits analysis at a start pose P and proceed along the frontier, countingthe cells on the frontier that have not been covered. If the countreaches a number indicated by the limitation in PC1, and the otherlimitations of PC1 are met, the mobile device has found a frontier,starting at P, that satisfies PC1. This is one way a map cell count canbe a proxy for a length parameter. Other analyses disclosed herein mayalso be performed using the map and based in whole or in part oninformation in the map.

PC1 may also have minimum length requirements, similar to those of SC1and SC2 (e.g. less than ¾ of the diameter of the mobile device, 20 cm, amobile device diameter, etc.). These values may also be stored, in theSC and PC constraints, as cell counts. Benefit of having a minimumlength constraint or limit in the constraints include, but are notlimited to, avoiding exploration of small or insignificant open spaces,avoiding interrupting a covering routine to cover a small region(because, e.g., doing so may look unexpected to an observer), andaccounting for noise in the map (e.g., small gaps in the map that resultfrom sensor deviations and which may indicate map frontiers that do notcorrespond to frontiers in the actual surface).

Unexplored regions may be treated similarly to occupied portions of thesurface in this analysis for at least two reasons. One is that themobile device may have only sparse information about obstacles due tothe traversal path of the mobile device during region based covering.Another is that some embodiments may implement perimeter covering toexplore previously unexplored portions of the surface. Unexploredportions of the surface may be reasonably likely to contain obstacles(e.g., they are often unexplored because they are proximate toobstacles) and if they are not completely comprised of obstacles thenexploration into those portions of the surface is desired in someembodiments, such as those seeking to maximize coverage.

At state 315, a decision is made based on whether the frontierenumeration of state 310 enumerated or identified any frontierssatisfying PC1. If no suitable frontiers are found then the perimetercovering routine 300 terminates with ending condition “no perimeterfrontiers” at state 370. In illustrated process 100, this leads to thetermination of that run of the covering process 100 at state 160. Iffrontiers are found, a frontier Fr1 which optimizes function Fn1 isselected for covering at state 320. Fn1 is a costing or ranking functionwhich may optionally be similar to those that have been previouslydiscussed.

For example, the ranking function may rank the identified or enumeratedfrontiers based on parameters including distance from current pose ofthe mobile device to the frontier or cost in power or time to reach thefrontier, frontier length (where a longer frontier may receive a heavierweight), and/or quality of a localization signal along the frontier(e.g., where better quality signals may receive a higher weight, but insome embodiments a lower quality signal may be selected first if, forexample, the ability to process a weak signal degrades the longer themobile device operates). The top ranking frontier according to Fn1 iscovered first. Other embodiments may be select from the availablefrontiers at random or in other fashions. One embodiment uses distanceto the frontier as the only factor; other embodiments may usecombination of other parameters.

Once a frontier is selected in state 320, at state 325 the mobile devicenavigates to the starting location of the frontier and engages inperimeter following or covering at state 330. Once in perimeter coveringmode, the mobile device executes a loop comprising states 335, 340, 345,350, and 355. The mobile device follows the perimeter at state. 335while periodically evaluating the frontier originating from the currentmobile device position at 340 to determine when to terminate perimeterfollowing. Following the perimeter, in some embodiments, is performed byusing sensors associated with the mobile device to detect the source ofthe perimeter (e.g., a weak signal or a physical obstacle) and tonavigate along that source, for example by repeatedly moving againstthat source and away from it, with a bias tangential to the source. Thisis one way in which a mobile device may update, correct, or otherwiseaugment information in the map. For example, if the map falselyindicated that location was occupied, some embodiments' perimeterfollowing might correct that data because the process of following thesource of the perimeter will cause it to move into logically occupiedlocations.

At state 340, the mobile device examines the frontier originating at thecurrent mobile device location to determine if its previous action hascreated a frontier which is suitable for region based covering accordingto previously discussed constraint SC1. In some embodiments, aconstraint other than SC1 may be used in state 340. If the frontiersatisfies the constraint then the perimeter covering routine 300 endswith condition “snake created” at 365 and control may pass to regionbased covering with start condition “cover created snake” per states 140and 250 of processes 100 and 200, respectively. Otherwise, perimetercovering continues per state 335.

FIG. 3 shows that states 350 and 355 occur next after state 345 if theconstraint is not satisfied. Some embodiments may operate this way. Moregenerally, states 340 and 345 and states 350 and 355 are runperiodically while the mobile device continues to cover the perimeterper state 335. For example, states 340 and 345 and states 350 and 355may run at set times or after the mobile device has moved a specifieddistance. The pairs of states may alternate regularly, multipleiterations of one pair may run before an iteration of the other pair, orthe pairs of states may be performed in a more complicated pattern oraccording to another algorithm.

In any case, at state 350 the mobile device evaluates the frontieroriginating from the current mobile device's current location accordingto constraint PC2 to determine if the frontier perimeter covering shouldcontinue. Constraint PC2 may be like constraint PC1 in that it selectsfrontiers between explored portions of the surface and occupied and/orunexplored portions, which have not been previously perimeter covered,do not leave the map, and are not in portions of the surface in whichthe mobile device does not detect sufficient localization signal, forexample. A difference between the two constraints may be that PC2 isless strict than PC1. For example, PC1 might select only those portionsof the perimeter that are at least a meter long, while PC2 might simplyselect those that have a shorter distance, such as 20 cm, or one or twomap cells, ahead of them that have not been perimeter-covered. In thisway, the perimeter covering routine, once it identifies a perimeterportion that satisfies PC1, will continue on that portion so long as itsatisfies PC2. Some embodiments may do this for the purpose ofhysteresis—if PC1 and PC2 were the same or not sufficiently different,then perimeter covering might halt once sufficient portions of aperimeter had been covered so as to make PC1/PC2 fail and relativelylittle of the perimeter would actually be covered by perimeter covering.

When the mobile device begins to cover portions of the perimeter it hasalready covered, attempts to traverse a border of the surface, orapproaches a previously discovered portion of the surface known to havea poor localization signal (for example), constraint PC2 will begin tofail, and at state 355 the mobile device will decide to terminate atstate 360 with ending condition “perimeter covered”. In this case, someembodiments of a control process 100, such as the one illustrated, willcheck to see if region based covering is possible anywhere in the map orsurface by invoking region based covering with start condition “coveranywhere”, such as state 140 of process 100 invoking state 225 ofprocess 200.

Example of Room Coverage

FIGS. 7 through 14 show an example of a mobile device covering accordingto the present disclosures. FIG. 7 shows a top view plan of a room 700containing some furniture (705-717) inside and a mobile device atinitial pose 720. The mobile device has been placed on the floor andinstructed to start the covering (e.g., via direct interaction with themobile device such as by pressing a button or using a remote control, orvia indirect action such as a timer or a programmatic interface). State110 of the covering routine 100 is executed. The map is essentiallyempty of content and in some embodiments the map has no cells. In otherembodiments the cells are all uninitialized or marked as unexplored. Themobile device has no or substantially no information about the roomlayout and the location of the furniture.

Referring to FIG. 8, the mobile device executes state 120 and invokesregion covering with “cover to right”. According to process 200, abounding box 810 for a region 1 is established. The boundary 810 isshown as a dashed line and happens to extend beyond the room's 700borders. The mobile device executes a snaking action that results in itfollowing path 850. As the mobile device travels along the current rankit enters information in the map about the portions of the region thatit was able to traverse without bumping into obstacles (marking thoselocations 830 as covered/traversed). When the mobile device bumps intoor otherwise detects an obstacle such as a wall or furniture, it marksthe estimated location of the obstacle 840 as occupied and follows theedge of the obstacle until it reaches the next rank. The mobile devicethen travels along that rank in a direction opposite to the previousrank direction of travel.

As shown in FIG. 8, the mobile device travels outside of the room 700through a door 725, but it is able to detect that it has left the roombecause a localization signal becomes attenuated below a predefinedthreshold in surface portion 820. When this is detected, the mobiledevice turns/rotates around. In one embodiment, sensing localizationsignal attenuation is implemented by measuring the level of one or moreinfrared localization signals that are projected onto the ceiling ofroom 700 and detecting that the level has decreased below a predefinedlevel. In another embodiment, the user can place a “virtual boundary” inthe proximity of a door, for example as illustrated if FIG. 17 anddiscussed in the contact of that figure, below.

The mobile device completes covering region 1 and exits the regioncovering routine because there are no more snake frontiers to coverinto. The frontiers along the left and right walls of the room 700(indicated as the non-filled room borders within the region 810) do notsatisfy the relevant SC2 criteria because they are too small, and thefrontier along the top of the region does not satisfy the criteriabecause it is in the wrong direction (i.e., map analysis or otheranalytics show it to open in the north direction, but mobile device iscurrently exploring in the south direction).

The mobile device then proceeds to state 130 and invokes region coveringwith start condition “cover to left”. This is illustrated in FIG. 9. Anew region 1 is established with bounding box 910. The snaking actionends with the mobile device at location 920 when the mobile devicereaches the top of the bounding box for region 1 and there are no moreinternal frontiers that can be covered by snaking.

FIG. 10 illustrates an example of the mobile device and map as themobile device covers a second region (a region 2) during the executionof regional covering invoked with “cover to left”. This figure showsthat while covering to the left of obstacle 705, an interference in thelocalization signal causes the mobile device to improperly record thelocation of the wall 1040 in the map. A similar effect could have othercauses, such as a degrading localization routine or a mechanicalmalfunction that temporarily causes the mobile device to move at anangle instead of vertically (a malfunction that is remedied, perhaps, bythe mobile device bumping into obstacle 705). A similar effect may alsoresult if a person, pet, or other transient obstacle is present. In anycase, the map indicates, erroneously, that 1030 is not a frontier but isan edge of an occupied portion of the surface. As a consequence of thaterror, the mobile device terminates region covering even though there isstill some portion of the surface in the region that can be covered. Themobile device then performs state 140, but exits with end condition “NoFrontiers” upon analyzing the map and determining that there are no morefrontiers to be covered (because, again, none of the potential frontiersare sufficiently large to meet the relevant criteria).

Referring to FIG. 11, the mobile device enters state 150 and invokesperimeter covering. The mobile devices moves to position 1120 based on acost evaluation function and analysis of the map, and starts perimetercovering around the furniture. The perimeter covering routine causes themobile device to move past the erroneous obstacle location because insome embodiments perimeter following/covering is purely reactive to theobstacles once it has begun. Map analysis selected a perimeter portionto cover, but the embodiment relied on physical sensors to continuefollowing the obstacle and updated the map based on its observations.Moving past the erroneous obstacle location 1030 creates a new frontierthat can be covered by snaking action. When the perimeter coveringroutine detects a new snake frontier that satisfies SC1 the perimetercovering routine exits with end condition “snake created”.

Referring to FIG. 12, the covering control routine 100 loops back intoregion covering with start condition “cover created snake”. The mobiledevice snakes starting along the large frontier created by the perimetercovering action 1110 of FIG. 11.

Referring to FIG. 13, a second frontier that qualifies for snakecovering is located in the map. The mobile device moves to that frontierfollowing path 1310 and performs a snaking action. Then there are nomore frontiers that qualify for snake covering. Region covering existsand perimeter covering is re-entered.

Referring to FIG. 14, the mobile device covers all the perimeterportions that had not been covered during the previous perimetercovering action. No new snakable frontiers are created by the perimetercovering action in this example. The control routine 100 exits at state160.

Dynamic Resizing of Covering Region

As disclosed above, the definition of regions and their bounding boxescan vary amongst embodiments and even in a single embodiment. By way offurther example of dynamic regions, regions may be defined andinformation about them stored in the map before the mobile deviceacquires any knowledge about the surface, including its layout. In someembodiments, these predefined regions may be defined in such a way thatthe mobile device does not extend its ranks from one (unknown) wallborder to an opposing (unknown) wall border because the region does notencompass both borders. The result may be a snaking action and coverageroute that is not as logical or predicable to, for example, a humanobserver. FIG. 15(B) illustrates one such situation. The region has apredefined fixed size and when the bounding box 1520 is located relativeto the location 1530 of the mobile device, the region does not includeor extend beyond lower wall 1510.

In an example of an embodiment with dynamically resized regions, aninitial bounding box 1520 (for example, one 2 m×1.5 m) may beestablished. However, the length of the region is extended as the mobiledevice starts traversing the ranks 1540 until an obstacle is sensed inthe path of the mobile device, at which point the region stops expandingand has a final dimension as illustrated in FIG. 15(B).

Deferred Coverage

In some surface configurations, region based covering as illustrated inFIG. 2 and described above may cause a mobile device to travel largedistances to reach the frontiers. An example is illustrated in FIG. 16.A kitchen isle 1610 splits the current region1 1620 into two halves suchthat no path exists within the region to go from point A to point B.Assuming that during exploration/covering of 1605, the mobile devicediscovered frontiers F_(A) and F_(B). According to the illustratedprocesses 100, 200, 300, and 500, after covering the frontier F_(A) ofRegion 1, the mobile device would have to travel back over the coveredportion of the surface to reach frontier F_(B). In an embodiment withdeferred coverage, the mobile device will instead add frontier F_(B) to,for example, a list of deferred frontiers and proceed to C. The order ofcoverage may then be A, C, B, D. The alternative order, without deferredcoverage, might be A, B, D, C (or even A, B, C, D). Both alternativesinvolve move travel over previously explored space than using deferredcovering and result in behavior that is less surprising to observers.Embodiments with deferred coverage may have a snaking or traversalprotocol that takes this into account.

In one embodiment, the overall covering efficiency and mobile devicepredictability is increased by deferring covering some of the portionsof a region. For example, the mobile device may decide to defer coveringof a frontier if the “cost” to cover that frontier is too high, giventhe current state of the mobile device. This cost can be the ratio ofthe distance to the frontier and the length of the largest snake rankperformed in the current region or other metrics, including those thatincorporate resource costs or time. Deferred frontiers may be stored ina list in a similar fashion to the map or as part of the map. They maybe covered by the mobile device once it has completed region-basedcovering. The mobile device can again decide which deferred frontier ismost optimal to cover first, given its current state and knowledge ofthe surface as embodied in the map. Various metrics such as thosediscussed above may be used. For example, in one embodiment, thedistance to the frontier start is the metric used.

Restricted Coverage

A restricted covering mode allows some embodiments to prioritizecoverage of certain portions of a surface over others. Other restrictedcovering modes prevent the mobile device from exploring certain portionsof the surface. Such a mode may be used to, for example, prevent amopping robot from covering (and mopping) a carpeted portion of floor. Amobile device configured with a localization system can be made to coverwithin (or avoid) a restricted portion of the surface without the needfor any external intervention (such as by a user) through the use ofremovable or temporary signal emitters. For example, depending on theconfiguration of the mobile device and what type of signal sensors ithas, strategically placing IR emitters or magnetic strips may create avirtual boundary which a mobile device will not pass.

In one such embodiment, illustrated in FIG. 17, a mobile device withinitial pose 1740 is restricted to cover only the upper right quadrant1710 with respect to initial pose 1740. The coverage proceduresdescribed above can be adapted to fit this constraint by treating thedetection of a virtual wall 1730 an obstacle and thereby preventing amobile device from passing through it. For example, by placing themobile device on one side or the other of the virtual walls 1730, a usercan control whether the mobile device operates within region 1710 oroutside it.

Overlapping Coverage

In some instances it is advantageous to reduce or minimize overlapbetween regions so as to avoid repeated traversing of the same locationand to thereby finish coverage sooner and/or with less expenditure ofresources such as power and any consumables such as cleaning suppliesused by the mobile device. Even in some such instances, a variety offactors may result in overlap among regions. Some such overlap may beintentional, for reasons similar to what has been discussed in thecontext of navigation and ranks. For example, an embodiment may defineregions that overlap with one another for aesthetic or functionalrequirements (e.g., those related to mopping or sweeping functions) suchas helping regions appear to “blend” into one another or ensuring thatseams between regions are covered. Some embodiments may intentionallydefine overlapping regions to help account for discrepancies between themap and the actual surface. An embodiment which defines regions on a mapthat inaccurately reflects the surface (for example, due to accumulatedsensor error or other factors discussed above) may intentionally defineoverlapping regions to help compensate for such error. Yet anotherembodiment may not define overlapping regions on a map, but will cause amobile device to cover overlapping surface locations because, forexample, of errors in the map. Still another embodiment may defineoverlapping regions to facilitate other aspects of covering. Forexample, a non-overlapping region may be too small to allow snaking, soa larger region, which overlaps adjacent regions, may be defined. Theseare merely illustrative examples of why, even in embodiments with a biastowards non-overlapping regions, there may still be 10, 25, 33, 50, orsome other percent overlap between any two regions.

However, in certain situation (i.e., particular surface layouts,possibly in conjunction with particular starting positions) coverageroutines such as those described above may still systematically neglecta portion of a surface such as by consistently failing to detect atheoretically reachable portion of the surface.

This potential risk can be mitigated by some embodiments which performoverlapping (and thus theoretically redundant) coverage routines. In onesuch embodiment, a mobile device is configured to perform “criss-cross”coverage by making two additional calls to region based cleaning process200 before states 135 and 140. Whereas the previously described “coverright” and “cover left” invocations involve a rotation of 90 degreesclockwise and 90 degrees counterclockwise, invocation of region-basedcleaning with “cover down” and “cover up” involve a rotation of 180degrees a second rotation of 180 degrees. The processes can otherwise beanalogous to those previously described. The result is a coveragestrategy as illustrated in FIG. 18. In addition to covering right andleft halves of the surface, as shown in FIG. 18A and FIG. 18B, such amobile device covers top and bottom halves of the surface as shown inFIG. 18C and FIG. 18D. In general, the four invocations could be made inother orders. The invocations may be followed by open region coveringand perimeter covering, as previously described.

Dividing a surface into four overlapping halves allows a mobile deviceto cover the same areas in two orthogonal directions. Such criss-crosscoverage may have other advantages in particular embodiments. Forexample, it can reduce streaking patterns left on floors by cleaningrobots from the drying out of cleaning fluid and allow lawn mowingrobots or vacuuming robots to create more aesthetically pleasingpatterns.

Physical Components

FIG. 4 illustrates example physical components of an appropriatelyconfigured mobile device. Such a device may include dead reckoningsensors 490 and/or signal sensors 470. These sensor components maycommunicate with one or more processors 410. The processor may be, forexample, a specially configured chip or a more general processorconfigured through software. The processor may include its own storageand/or the device 400 may include additional memory or storage 420(e.g., to store software and the data to implement some or all of themethods described herein). In some embodiments the sensors 470 and/or490 may also store data directly in the memory 420. Software forimplementing aspects of what is disclosed may be stored in ROM, flashmemory, magnetic memory, optical memory, and/or some other form ofpersistent storage, although volatile storage (e.g., RAM) may be used aswell. Data may be stored in volatile (e.g., can be erased when thesystem powers down) and/or non-volatile memory (which stores the datafor later access even if the device is powered down and then powered upagain). The processor 410 and storage 420 may also be used forfunctional purposes not directly related to localization. For example,the mobile device 100 may use the processor 410 and storage 420 whenperforming tasks such as cleaning or guarding or when interpreting datafrom the sensors 470 and 490. In other embodiments, the processing 410and storage 420 are dedicated to covering and the device containsadditional computational capacity for other tasks.

The sensors 490 may include a wide range of dead reckoning sensors,motion sensors, radar and sonar type devices, and other forms ofobstacle detection. There may also be dedicated obstacle detectors, andthe corners may be outfitted with corner detectors or the like. Forexample, an accelerometer 495 may be present.

The processor 410 and or storage 420 may be operatively connected tovarious output mechanisms such as screens or displays, light and soundsystems, and data output devices (e.g., busses, ports, and wireless orwired network connections). Mobile device 400 is show with a port, suchas a USB port, at 425. The processor 410 and/or the storage 420 is alsooperatively connected to a locomotion system which may include wheels480, or other forms of locomotion such as tracks or fins and rudders anda propulsion source. Movement may involve in signals being sent tovarious controllers such as motors (including drive motors orservomotors), brakes, actuators, etc., which may cause the mobile deviceto move to a new pose (or to perform another activity, such as acleaning function). The move to this new pose may, in turn, triggeradditional output from the sensors to the processor. An exampleembodiment is configured with an ARM7 processor, 256K of flash ROM forsoftware, and 64K of RAM for data. These are not minimum or maximumrequirements some or all of what is disclosed herein can be accomplishedwith less or more processing and storage capacity. Other embodiments maybe different processors and different memory configurations, with largeror smaller amounts of memory.

Mobile device 400 is also shown with a power supply 430, a control panel405 for user input. More or fewer components, including but not limitedto functional components such as for cleaning or performing other tasks,may also be present.

Broadly Applicable

The systems and methods disclosed herein can be implemented in hardware,software, firmware, or a combination thereof. Software can includecompute readable instructions stored in memory (e.g., non-transitory,tangible memory, such as solid state memory (e.g., ROM, EEPROM, FLASH,RAM), optical memory (e.g., a CD, DVD, Bluray disc, etc.), magneticmemory (e.g., a hard disc drive), etc., configured to implement thealgorithms on a general purpose computer, special purpose processors, orcombinations thereof.

While certain embodiments may be illustrated or discussed as havingcertain example components, additional, fewer, or different componentsmay be used. Further, with respect to the processes discussed herein,various states may be performed in a different order or substantially inparallel, not all states are required to be reached, and fewer,additional, or different states may be utilized.

Various aspects and advantages of the embodiments have been describedwhere appropriate. It is to be understood that not necessarily all suchaspects or advantages may be achieved in accordance with any particularembodiment. Thus, for example, it should be recognized that the variousembodiments may be carried out in a manner that achieves or optimizesone advantage or group of advantages as taught herein withoutnecessarily achieving other aspects or advantages as may be taught orsuggested herein. Further, embodiments may include several novelfeatures, no single one of which is solely responsible for theembodiment's desirable attributes or which is essential to practicingthe systems, devices, methods, and techniques described herein.

What is claimed is:
 1. A mobile device configured to navigate a surface,the mobile device comprising: a movement mechanism configured to movethe mobile device among poses on the surface, each pose comprising adevice location and a device orientation; a mapping module configured toupdate a map representing data about the surface, the map associatingmap locations with one or more properties sufficient to indicateunexplored, explored, and occupied locations, wherein a frontierindicates a boundary between an explored location and an unexploredlocation, and an edge indicates a boundary between an explored locationand an occupied location; an initialization module configured toestablish an initial pose; a first region-covering module configured tocause the movement mechanism to move the mobile device relative to oneor more first frontiers discovered in a first direction of regiondiscovery so as to cover a region of the surface and to cause themapping module to update the map; a second region-covering moduleconfigured to cause the movement mechanism to move the mobile devicerelative to one or more second frontiers discovered in a seconddirection of region discovery so as to cover at least one additionalregion of the surface and to cause the mapping module to update the map;an edge-following module configured to cause the movement mechanism tomove the mobile device along edges, and to cause the mapping module toextend edges and add frontiers discovered as the mobile device movesalong edges, and a third region-covering module configured to cause themovement mechanism to move the mobile device relative to third frontiersdiscovered in the course of moving the mobile device along edges,wherein the edge-following module initiates after at least one of thefirst, second, or third region-covering modules completes discoveringrespective first, second, or third frontiers, and wherein when nofurther frontiers are discovered by any of the first, second and thirdregion-covering modules, the edge-following module causes the movementmechanism to again move the mobile device along at least some edgespreviously followed.
 2. The mobile device of claim 1, wherein each ofthe modules comprises a computerized system.
 3. The mobile device ofclaim 2, wherein the respective modules are comprised of a single commoncomputerized system.
 4. The mobile device of claim 1, wherein themovement mechanism comprises one or more wheels.
 5. The mobile device ofclaim 1, wherein the movement mechanism comprises one or more tracks. 6.The mobile device of claim 1, wherein the movement mechanism comprisesat least a rudder component and at least a propulsion component.
 7. Themobile device of claim 1, wherein the mapping module associates alocation with one or more properties based at least in part oninformation from one or more sensors associated with the mobile device.8. The mobile device of claim 7, wherein the mapping module associates alocation with traversed if the sensors indicate that the mobile deviceis in or has moved through that location.
 9. The mobile device of claim7, wherein the mapping module associates a location with occupied if thesensors indicate that mobile device cannot move into that location. 10.The mobile device of claim 7, wherein an edge comprises one or morelocations associated with “edge” and one or more locations notassociated with “edge”.
 11. The mobile device of claim 7, wherein theedge-following module is further configured to rely at least in part ondata from the sensors to follow the edge.
 12. The mobile device of claim11, wherein the edge-following module is further configured to cause themapping module to remove an association between a location and “edge”.13. The mobile device of claim 1, wherein the mapping module associatesa location with edge if an adjacent location is occupied.
 14. The mobiledevice of claim 1, wherein the mapping module associates a location withunexplored if the location is adjacent to a traversed location and isnot occupied or traversed.
 15. The mobile device of claim 1, wherein aregion is covered if at least 90% of what is accessible to the mobiledevice is associated with a traversed location on the map.
 16. Themobile device of claim 1, wherein a region is covered if at least 80% ofwhat is accessible to the mobile device is associated with a traversedlocation on the map.
 17. The mobile device of claim 1, wherein a regionhas a definition which is independent of properties of the surface. 18.The mobile device of claim 1, wherein each region is a proper subset ofthe surface.
 19. The mobile device of claim 1, wherein a region hasstatic dimensions.
 20. The mobile device of claim 1, wherein a regionhas at least one dynamic dimension.
 21. The mobile device of claim 20,wherein a region has at least one dynamic dimension determined at leastin part by at least one dimension of a second region.
 22. The mobiledevice of claim 1, wherein a first region and a second region arenon-overlapping if less than 10% of the first region is in the secondregion.
 23. The mobile device of claim 1, wherein a first region and asecond region are non-overlapping if less than 25% of the first regionis in the second region.
 24. The mobile device of claim 1, wherein afirst region and a second region are non-overlapping if less than 50% ofthe first region is in the second region.
 25. The mobile device of claim1, wherein the edge-following module is configured to cause the movementmechanism to move the mobile device so as to cover an edge-discoveredregion if, while following an unfollowed edge, at least one location notassociated with “edge” is traversed.
 26. A method for navigating asurface with a mobile device, the method comprising: defining areference frame using a computing device, based on at least a componentof a first pose of a mobile device on a surface having one or moreborders and containing one or more obstacles, the first pose comprisinga first position and a first orientation; exploring relative to one ormore first frontiers discovered in a first direction of regiondiscovery, by the mobile device, a first region of the surface so as tocover the first region of the surface, the first region determined basedat least in part on a component of the first pose, wherein a frontierindicates a boundary between an explored location and an unexploredlocation; exploring relative to one or more second frontiers discoveredin a second direction of region discovery, by the mobile device, atleast one first additional region of the surface, so as to cover the atleast one first additional region of the surface after covering thefirst region; maintaining a map of information about the surface incomputer readable memory, wherein at least a portion of the informationis obtained by exploring the first region and the additional region; andperimeter-following one or more unfollowed perimeter portions to extendperimeters and add frontiers discovered as the mobile device moves alongperimeters, wherein a perimeter corresponds to a boundary between anexplored location and an occupied location, when analysis of the mapindicates one or more unfollowed perimeter portions exists by:navigating the mobile device to a first position on a first perimeterportion that is unfollowed; following the first perimeter portion,relying at least in part on one or more sensors to determine how tofollow the first perimeter portion; updating the map to indicate thatthe followed first perimeter portion is followed; and updating the mapwith additional information about one or more locations traversed whilefollowing the first perimeter portion; wherein the perimeter-followinginitiates after discovery of the first frontier is complete, or afterthe discovery of the second frontier is complete, or after both thediscovery of the first frontier and the second frontier is complete; andexploring unexplored second additional surface regions discovered whileperimeter-following; wherein exploring a region comprises: navigatingthe mobile device in the region; updating the map to indicate one ormore discovered perimeters, perimeters comprising surface borders andobstacle boundaries, when such are identified; and updating the map toindicate that traversed portions of the surface have been exploredwherein when no further frontiers are discovered, moving the mobiledevice along at least one perimeter previously followed.
 27. The methodof claim 26, wherein the mobile device performs localization using asignal based localization system which uses detected signal information,wherein the signal is broadcast from a broadcast device.
 28. The methodof claim 26, wherein exploring unexplored additional surface regionsdiscovered while following the first perimeter portion is performed whenthe map indicates no unfollowed perimeter portions exist.
 29. The methodof claim 26, wherein exploring unexplored additional surface regionsdiscovered while following the first perimeter portion is performedwhile the map indicates unfollowed perimeter portions exist.
 30. Themethod of claim 26, wherein the at least one additional region isdetermined based at least in part on a part of the first pose.
 31. Themethod of claim 26, wherein the at least one additional region isdetermined based at least in part on the first region.
 32. The method ofclaim 26, further comprising, after first performing the steps of claim26: configuring the mobile device on the surface with the first pose;and performing the steps of claim 26 a second time; wherein the behaviorof the mobile device is substantially similar during the firstperforming and the second performing.
 33. The method of claim 26, wherethe surface is the floor of a first room.
 34. The method of claim 26,where the first region and all additional regions collectively comprisemore than 90% of the surface.
 35. The method of claim 26, whereinnavigating the mobile device through a region comprises snaking throughthe region.
 36. The method of claim 26, wherein navigating the mobiledevice through a region comprises spiraling through the region.
 37. Themethod of claim 36, wherein navigating the mobile device through aregion comprises outward spiraling through the region.
 38. The method ofclaim 26, wherein there is substantially no portion of the surface thatis in both the first region and a second region.
 39. The method of claim26, wherein there is substantially no portion of the surface that is inmore than one region.
 40. The method of claim 26, wherein no more than10% of the first region is also in a second region.
 41. The method ofclaim 26, wherein a first border of the surface is detected based ondistance travelled by the mobile device.
 42. The method of claim 26,wherein a first border of the surface is detected based on detection ofan obstacle.
 43. The method of claim 26, wherein a first border of thesurface is not a physical border.
 44. The method of claim 43, whereinthe first border of the surface is detected based on comparing a valueof a signal to a threshold.
 45. The method of claim 26, wherein a firstborder of the surface is a wall of a room.
 46. The method of claim 26,wherein the mobile device is a cleaning device.